UNIVERSITY  OF  CALIFORNIA  agricultural  Experiment  Station 

College  of  agriculture  e.  j.  wickson,  act.ng  director 

BERKELEY,   CALIFORNIA 


CIRCULAR  No.  23 

(August,  1906.) 


PURE  YEAST   IN   WINERIES. 


BY 

FREDERIC  T.  BIOLETTT. 


While  in  the  present  state  of  the  wine-making  industry  and  of  the 
general  lack  of  knowledge  among  wine  makers  of  the  principles  of 
fermentation,  the  use  of  pure  yeast  is  not  to  be  universally  advocated, 
there  are  many  cases  in  California  where  it  can  be  of  great  utility. 

Both  laboratory  and  cellar  experiments  on  a  sufficiently  large  scale, 
and  continued  for  a  sufficiently  long  time,  have  fully  demonstrated 
that  most  excellent  results  can  be  obtained  by  the  use  of  pure  yeast. 
This  is  especially  true  as  regards  white  wine. 

The  principal  benefits  to  be  obtained  at  present  are  a  thorough 
fermentation,  a  rapid  clearing  and  an  absence  of  the  disagreeable 
flavors  of  secondary  fermentation,  which  are  only  too  common  in  many 
of  our  Californian  wines.  These  benefits  are  to  be  obtained,  however, 
in  cellars  only  where  especial  care  in  the  ordinary  processes  of  wine- 
making  are  at  present  practised.  In  many  of  the  larger  wholesale 
wineries,  or  in  those  where  ordinary  carefulness  is  not  exercised,  little 
benefit  would  result  from  the  use  of  pure  yeast.  There  are  other  much 
more  important  reforms  to  be  introduced  first.  The  great  improve- 
ments in  methods  which  have  been  introduced  in  late  years  in  certain 
large  wineries,  however,  make  it  probable  that  before  long  many  of 
them  will  be  in  a  position  to  make  use  of  the  advantages  of  pure  yeast. 

For  this  reason  it  is  advisable  that  the  methods  of  handling  pure 
yeast  practically  in  wine-making  should  be  made  familiar  to  the  wine- 
makers  of  small  cellars  where  it  is  at  present  feasible.  This  circular 
is  issued,  therefore,  with  the  hope  of  interesting  some  of  the  more 
progressive  wine-makers  in  this  method  of  improving  their  product. 

It  should  be  clearly  understood  at  the  beginning  that  the  purity 
of  the  yeast  is  of  less  importance  than  its  character.  The  yeast  must 
be  of  the  right  kind.  Beer  yeast  will  give  a  flavor  of  beer,  and  will, 
moreover,  fail  to  transform  all  the  sugar,  leaving  a  half  fermented 
liquid  that  will  inevitably  spoil.  Bread  yeast,  apiculate  yeast,  any  of 
the  innumerable  species  of  yeast  that  occur  in  fermenting  liquids, 
will  simply  injure  the  wine.  Even  the  true  wine  yeast  has  many 
varieties,  each  with  its  own  qualities,  and  it  is  unsafe  to  use  any  pure 
yeast  until  it  has  been  properly  tested  for  the  purpose  contemplated. 
The  yeast  must  be  obtained,  therefore,  from  a  perfectly  reliable  source, 


where  it  has  been  proved  suitable  for  the  conditions  in  which  it  is 
to  be  used.  An  unsuitable  or  untested  yeast  is  as  sure  to  give  unsatis- 
factory results  in  the  fermenting  vat  as  a  lot  of  seedlings  in  the  peach 
orchard. 

On  the  other  hand,  the  best  results  are  to  be  obtained  only  if  our 
original  stock  is  perfectly  pure.  If  the  stock  is  contaminated  with 
vinegar  germs,  wine-flowers,  or  molds,  it  may  do  more  harm  than 
good.  The  effect  would  be  similar  to  that  obtained  by  planting  wheat 
seed  mixed  with  cheat  or  alfalfa  seed  with  dodder. 

For  these  reasons  the  Experiment  Station  has  selected  and  tested 
a  number  of  yeasts  which  have  been  under  observation  for  several 
years,  and  is  ready  to  recommend  one  for  use  in  practice  which  has 
uniformly  given  good  results.  We  are  prepared  to  supply  small  quan- 
tities of  this  yeast  in  an  absolutely  pure  state  to  a  limited  number  of 
wine-makers  for  use  during  the  present  season. 

If  the  directions  of  this  circular  are  carefully  followed,  good  results 
will  be  obtained,  provided  nothing  is  done  to  counteract  them.  Pure 
yeast,  however,  will  not  overcome  altogether  the  effects  of  infected 
vats  and  casks,  nor  will  it  enable  the  wine-maker  to  produce  Chateau 
Lafite  from  raisins,  and  above  all,  it  will  not  aid  him  in  the  vital  point 
of  cool  fermentation.  If,  however,  the  usual  precautions  known  to  all 
good  wine-makers  are  taken,  pure  yeast  will  give  satisfactory  results. 

The  principal  things  to  be  kept  in  mind  are  to  get  the  grapes  or 
must  into  the  vats  as  clean  as  possible,  to  introduce  the  starter  before 
any  spontaneous  fermentation  has  started,  and  to  control  the  tempera- 
ture. 

For  red  wine  some  such  cooling  device  as  that  described  in  Bulletin 
174  should  be  used,  unless  very  small  vats  are  employed  and  the 
fermentation  is  to  take  place  in  the  cooler  sections  of  the  State. 
Pure  yeast  is  particularly  valuable  when  used  in  connection  with  the 
method  of  making  red  wine  described  in  Bulletin  177.  For  white  wine 
good  results  will  be  obtained  in  almost  all  cases,  though  a  preliminary 
defecation  is  desirable.  This  defecation  may  be  obtained  by  the  use 
of  sulphur  fumes  or  of  meta-bisulphite  as  described  in  Circular  No.  22. 

The  small  quantity  of  pure  yeast  received  must  be  increased  by  the 
wine-maker  until  it  is  sufficient  for  a  "starter."  A  starter  is  a  quan- 
tity of  must  containing  young,  vigorous  yeast  in  sufficient  amount  to 
take  possession  of  the  vat  of  grapes  or  cask  of  must  before  the  germs 
naturally  existing  there  have  time  to  develop.  The  method  of  making 
this  starter  is  described  later. 

This  starter  must  be  relatively  pure.  It  is  always  used  when  in 
full  fermentation,  that  is,  when  it  contains  the  maximum  number  of 
pure  yeast  cells  and  before  the  weakening  of  the  yeast  has  allowed 
any  bacterial  or  other  spores  that  may  be  present  to  develop  or  in- 
crease. The  few  foreign  germs,  therefore,  which  may  get  into  the 
starter  during  the  last  manipulations  may  be  disregarded,  as  they  are 
in  such  an  infinitesimal  minority  that  they  have  no  chance  to  develop 
sufficiently  to  do  any  harm  before  the  wine  is  finished  and  safe  from 
their  attack.  With  ordinary  care  in  the  manipulation  of  the  starter 
they  will  be  incomparably  less  numerous  than  the  same  germs  existing 
naturally  in  the  crushed  grapes  to  which  the  starter  is  added. 


The  amount  of  yeast  added  must  be  sufficient.  As  a  rule  the  amounl 
of  starter  should  be  about  1%  of  the  volume  of  the  grapes  or  must 
to  be  fermented. 

If  the  grapes  have  been  partially  sterilized  by  heat  or  the  must  by 
defecation,  less  will  be  sufficient.  If  they  contain  considerable  amounts 
of  natural  germs,  more  will  be  needed.  If  the  infection  with  molds, 
yeasts  and  bacteria  due  to  bad  grapes,  unclean  crushers  or  unsound 
vats  is  considerable  no  practical  amount  of  pure  yeast  will  have  any 
effect.  The  addition  of  too  large  a  volume  of  starter  should  be  avoided, 
as  it  may  produce  too  rapid  and  violent  fermentation,  which  will  be 
difficult  to  control  even  with  cooling  machines. 

While  the  perfect  sterilization  of  the  grapes  and  must  is  at  present 
impracticable  and  unnecessary,  the  number  of  foreign  germs  present 
should  be  kept  as  low  as  possible.  Sufficient  freedom  from  such  germs 
is  obtained  in  the  manufacture  of  white  wine  by  settling,  sulphuring, 
or  other  means  of  defecating  the  must. 

In  the  heat-extraction  method  of  making  red  wine  (see  Bulletin 
177)  the  partial  sterilization  due  to  the  heating  accomplishes  the  same 
end.  With  the  ordinary  method  of  making  red  wine  this  end  can  be 
compassed  only  by  the  most  minute  attention  to  cleanliness  and  other 
means  of  preventing  the  entrance  of  undue  numbers  of  germs  into 
the  crushed  grapes.  If  grape  boxes,  crushers,  carriers,  pumps,  chutes 
and  vats  are  never  washed  and  are  coated  with  must  and  grape  skins, 
they  serve  as  propagating  grounds  for  yeasts  and  germs  of  all  kinds. 
Piles  of  dry  pomace  outside  the  cellar  or  scattered  on  the  surrounding 
roads,  supply  the  air  with  myriads  of  bacterial  spores.  Vats  of  grapes 
exposed  to  these  agents  of  infection  cannot  be  influenced  by  a  few 
buckets  of  pure  yeast. 

Directions  for  Use  of  Pure  Yeast. 

For  1000  gallons  of  crushed  grapes  or  of  must. 

Materials  needed : 

1. — A  3-oz.  flask  of  pure  tested  wine  yeast. 

2. — Half  a  gallon  of  sterilized  must,  about  10%  Balling,  in  a  one- 
gallon  demijohn. 

3. — Ten  gallons  of  defecated  must  in  a  25-gallon  tub  furnished  with 
a  good  cloth  cover. 

4. — A  room  comparatively  free  from  dust.  (For  example  a  moist 
cellar. ) 

Method  of  Procedure. 

First  Day. — Squeeze  out  a  quart  of  must  from  clean,  fresh  grapes. 
The  grapes  should  not  be  over-ripe.  Mix  the  must  with  a  quart  of 
boiled  water  and  place  the  mixture  in  a  sterilized  one-gallon  demijohn. 
The  demijohn  should  be  sterilized  by  thorough  cleaning,  and  heating 
for  an  hour  in  an  oven  or  rinsing  with  a  pint  of  10%  sulphuric  acid 
and  final  rinsing  two  or  three  times  with  boiled  water.  After  placing 
the  diluted  must  in  the  demijohn  close  the  latter  with  a  firm  plug  of 
cotton  wool  (surgeon's  cotton).  Place  the  demijohn  in  a  deep  covered 
pan  containing  water  such  as  an  ordinary  kitchen  wash  boiler  and  heat 
to  boiling  for  one  hour  and  then  put  aside  to  cool.  Do  not  remove 
cotton  plug. 


Second  Day. — 1.  Pour  a  few  drops  of  alcohol  onto  the  cotton 
plugs  and  necks  of  the  pure  yeast  flask  and  the  must  demijohn  and 
im  mediately  set  fire  to  the  alcohol.  This  will  destroy  any  spores  which 
have  settled  with  the  dust  on  the  plugs  and  necks.  After  shaking  the 
pure  yeast  flask  thoroughly  pull  out v  the  plug  and  pour  the  contents 
into  the  must  demijohn. 

Replace  the  plug  of  the  demijohn  and  shake  for  two  minutes  in 
such  a  manner  as  to  aerate  the  must.  Repeat  this  shaking  three  times 
a  day. 

Place  the  demijohn  in  a  warm  room  where  the  temperature  varies 
as  little  as  possible. 

2.  Defecate  10  gallons  of  must  from  clean,  fresh  grapes  containing 
not  over  22%  Balling. 

The  most  convenient  method  of  defecation  is  by  the  use  of  the 
sulphur  tapes  commonly  used  in  cellars.  In  a  12  to  15  gallon  keg  burn 
as  much  sulphur  as  the  air  present  will  consume.  (This  is  about 
J  of  an  ounce.)  Then  pour  about  4  gallons  of  perfectly  fresh  must 
into  the  keg,  bung  up  and  roll  for  5  minutes  to  make  the  must  absorb 
the  sulphur  fumes  and  finally  fill  the  keg  with  must,  taking  care  to 
mix  the  treated  with  the  untreated  must.  This  will  prevent  any  com- 
mencement of  fermentation  for  two  or  three  days,  if  the  must  is  kept 
in  a  fairly  cool  place. 

Chock  the  barrel  so  that  it  will  remain  steady  and  allow  the  impuri- 
ties of  the  must  to  settle. 

Third  or  Fourth  Day. — In  from  48  to  72  hours  the  must  in  the 
demijohn  should  be  in  full  fermentation  and  the  must  in  the  barrel 
should  be  perfectly  clear.  Draw  off  the  clear  must,  with  a  hose  steril- 
ized in  hot  water,  into  the  25-gallon  tub  which  should  also  have  been 
well  scalded.  Pour  the  fermenting  must  from  the  demijohn  into  the 
must  in  the  tub  and  thoroughly  aerate  the  mixture  by  dipping  out  some 
of  the  must  with  a  quart  dipper  and  pouring  through  the  air  back 
into  the  tub.  This  should  be  repeated  three  or  four  times  a  day,  or 
oftener  if  fermentation  is  slow  in  starting.  Fifteen  or  twenty  quarts 
should  be  poured  over  in  this  way  each  time. 

The  tub  of  fermenting  must  should  be  kept  in  a  warm  room  as  free 
as  possible  from  draughts  and  dust.  It  should  be  kept  carefully  cov- 
ered between  the  aerations,  to  exclude  dust. 

Sixth  or  Seventh  Day. — In  from  48  to  96  hours  after  starting,  the 
must  in  the  tub  should  be  in  violent  fermentation,  and  is  then  ready  to 
use  to  start  the  regular  fermentations.  The  volume  of  starter  used 
should  be  about  1%  of  the  volume  of  the  grapes  or  must  to  be  fer- 
mented. 

If  used  for  white  wine,  simply  pour  the  proper  quantity  of  starter 
into  the  cask  before  pumping  in  the  must.  If  used  for  red  wine,  the 
starter  should  be  distributed  through  the  vat  of  crushed  grapes  by 
pouring  in  a  little  at  a  time  as  the  vats  are  being  filled. 

If  it  is  desired  to  ferment  more  than  a  thousand  gallons  with  pure 
yeast,  special  directions  will  be  furnished  by  the  Station  on  request. 
Very  satisfactory  results  can  be  obtained  simply  by  starting  new  vats 
or  casks  with  1%  of  fermenting  must  from  one  of  the  first  fermenta- 
tions, which  have  been  started  with  pure  yeast,  when  it  is  in  full  action. 


